The present invention relates to a voltage generator which outputs a constant voltage irrespective of temperature or power source voltage changes, an output circuit for an error detector that is used for this voltage generator, and a current generator for outputting a predetermined current. More particularly, this invention relates to a voltage generator, an output circuit for an error detector, and a current generator constituted by bipolar transistors.
As a conventional voltage generator, there has been known a voltage generator structured by bipolar transistors. FIG. 8 is a diagram showing a schematic structure of a conventional voltage generator structured by bipolar transistors. This voltage generator consists of a reference voltage generator 54 for generating and outputting a constant reference voltage VREF irrespective of temperature or power source voltage changes, an error detector 55 having a negative-phase input connected to an output of the reference voltage generator 54, a PNP transistor 58 having an output of the error detector 55 connected to a base, having a high-potential side of the power source connected to an emitter, and having a collector connected to a voltage output terminal 53, a resistor 57 disposed between the voltage output terminal 53 and a positive-phase input of the error detector 55, and a resistor 56 disposed between the positive-phase input of the error detector 55 and a low-potential side (ground) 52 of the power source.
The reference voltage generator 54 generates a constant reference voltage VREF independent of a power source voltage and temperature. The reference voltage VREF can take only one value that satisfies a predetermined condition not to be independent of a power source voltage and temperature. As the reference voltage generator 54 has a large output impedance, an output voltage varies when a large output current flows. Therefore, only the reference voltage generator 54 is not sufficient for use as a voltage generator. Thus, the error detector 55, the PNP transistor 58, and the resistors 56 and 57 are also provided.
The PNP transistor 58 is disposed as an output buffer for obtaining a constant output voltage VREG8 independent of an output current, by reducing the output impedance. The error detector 55 is disposed as a feedback amplifier that inputs the reference voltage VREF and a feedback voltage VFBK from the reference voltage generator 54, amplifies the reference voltage VREF with a gain determined based on a ratio of a resistance R52 to a resistance R51 of the resistors 57 and 56, and outputs a voltage VOP. The output voltage VREG8 generated in the voltage output terminal 53 is expressed by equation 1.
VREG8=xe2x88x92(1+R52/R51)xc3x97VREFxe2x80x83xe2x80x83(1)
In other words, the output voltage VREG8 is determined based on the reference voltage VREF and a resistance ratio (R52/R51) between the resistors 56 and 57. As the reference voltage VREF has no dependency on temperature and a power source voltage, the output voltage VREG8 does not depend on temperature and a power source voltage either. Even when the output current increases, for example, the output voltage VREG8 is kept at a constant value shown in equation 1 based on a feedback loop of the feedback amplifier. When the error detector 55 operates from rail to rail, a set range of the output voltage VREG8 becomes as follows. A minimum side of the range is a voltage of a low-potential side 52 of the power source becomes, and a maximum side is a voltage (VCC-Vcesat) obtained by subtracting a collector/emitter saturation voltage Vcesat (generally, about 0.3 V) of the PNP transistor 58 from a voltage VCC of a high-potential side 51 of the power source.
In other words, the output voltage of this voltage generator is set within a range from a low power source voltage (a voltage at the low-potential side of the power source) to (VCC-Vcesat). In general, a current multiplication factor of a PNP transistor is as small as about HFE=20 to 50. Therefore, for driving a large current based on the output voltage VREG8, a large driving capacity is necessary for the error detector 55. When the current multiplication factor of the PNP transistor 58 is 20, and also when the driving current of the output voltage VREG8 is 100 mA, the error detector 55 needs to have an output stage that can bear an inflow current of 5 mA.
FIG. 9 is a diagram showing a schematic structure of another conventional voltage generator structured by bipolar transistors. This voltage generator has an NPN transistor 61 in place of the PNP transistor of the voltage generator shown in FIG. 8, and has the input polarity of the error detector 55 changed to the opposite polarity (the reference voltage VREF is input in the positive phase, and the feedback voltage VFBK is input in the opposite phase). This voltage generator also operates in a similar manner to that of the voltage generator shown in FIG. 8, and outputs an output voltage VREG9 determined by resistors 56 and 57. However, in general, the current multiplication factor of an NPN transistor is large (HFE=about 100). Therefore, in the case of this voltage generator, the current driving capacity of an error detector 55 may be small even when a large current is driven based on the output voltage VREG9.
For example, when a driving current of the output voltage VREG9 is 100 mA, it is sufficient that the input stage of the error detector 55 can bear the inflow current of 1 mA. When the error detector 55 operates from rail to rail, a set range of the output voltage VREG9 becomes as follows. A minimum value side of the range is a low power source voltage, and a maximum side is a voltage obtained by subtracting a base/emitter voltage Vbe (generally, about 0.9 V) of the NPN transistor 61 from a high power source voltage (a voltage at the high-potential side of the power source) In other words, the output voltage of this voltage generator is set within a range from the low power source voltage to (VCC-Vbe).
Further, it is also possible to construct a current generator by providing a current source circuit at a rear stage of the voltage generator. FIG. 10 is a diagram showing a schematic structure of a conventional current source circuit. This current source circuit consists of a voltage input terminal 71 connected to the voltage output terminal 53 of the voltage generator shown in FIG. 8 or FIG. 9, for inputting the output voltage VREG8 (or 9) of the voltage generator, a resistor 75 (a resistance R71) having one end connected to the voltage input terminal 71, an NPN transistor 73 having the other end of the resistor 75 connected to a collector and a base, a resistor 76 (a resistance R72) provided between an emitter of the NPN transistor 73 and a low-potential side 52 of the power source, an NPN transistor 74 having a base of the NPN transistor 73 connected to a base, and having a collector connected to a current output terminal 72, and a resistor 77 (a resistance R73) provided between an emitter of the NPN transistor 74 and the low-potential side 52 of the power source.
This current source circuit outputs a current based on an input of the constant voltage VREG8 (or 9) independent of temperature and a voltage power source. The NPN transistors 73 and 74 constitute a current mirror current source circuit. When the sizes of the NPN transistors 73 and 74 and the resistances R72 and R73 of the resistors 76 and 77 are of the same values respectively, an input current Iin8 and an output current Iout8 of the current source circuit can be expressed by equation 2.                                                                         I                ⁢                                  xe2x80x83                                ⁢                out                ⁢                                  xe2x80x83                                ⁢                8                            =                              I                ⁢                                  xe2x80x83                                ⁢                in                ⁢                                  xe2x80x83                                ⁢                8                                                                                        =                                                [                                      VREG8                    -                                          Vbe                      ⁡                                              (                                                  T                          ,                          Ie                                                )                                                                              ]                                /                                  (                                      R71                    +                    R72                                    )                                                                                        (        2        )            
In equation 2, Vbe (T, Ie) represents a base/emitter voltage of the NPN transistors 73 and 74 respectively, and this can be expressed as a function of temperature T and an emitter current Ie.
Temperature characteristic dVbe/dT of the base/emitter voltage Vbe (T, Ie) can be expressed by equation 3.
dVbe/dT=xe2x88x92{1.25xe2x88x92Vbe(T, Ie)}/Txe2x80x83xe2x80x83(3)
In equation 3, (1.25xe2x88x92Vbe (T, Ie) ) becomes a negative value. Therefore, a positive and negative relationship of the temperature characteristic dVbe/dT becomes opposite to that of the temperature T. In other words, the base/emitter voltage Vbe (T, Ie) has a negative temperature characteristic (a characteristic that the value decreases along a rise in temperature)
Assuming that the resistors 75, 76 and 77 do not have temperature dependency, the temperature characteristic dIout8/dT of the output current Iout8 is expressed as shown by equation 4 from equation 2.
dIout8/dT=xe2x88x92(dVbe/dT)/(R71+R72)xe2x80x83xe2x80x83(4)
In equation 4, a positive and negative relationship of (dVbe/dT) becomes opposite to that of the temperature T. Therefore, dIoutt8/dT has the same positive and negative relationship as that of the temperature T. In other words, the output current Iout8 has a positive temperature characteristic (a characteristic that the value increases along a rise in temperature).
The resistors 76 and 77 are inserted in order to restrict manufacturing variations in the base/emitter voltages Vbe of the NPN transistors 73 and 74 respectively. When the voltage between terminals of the resistors 76 and 77 is designed as large as possible, it is possible to restrict the influence of manufacturing variations in the base/emitter voltages Vbe. In the mean time, in order to secure a large operating bias voltage in the functional circuit to be connected to the current output terminal 72, it is desired to take a small operating bias voltage Vib for operating the current generator. When the collector/emitter saturation voltage of the NPN transistor 74 is expressed as Vcesat, the operating bias voltage Vib can be expressed by equation 5.
Vib=Vcesat+Iout8xc3x97R73xe2x80x83xe2x80x83(5)
In other words, when the voltage between terminals (Iout8xc2x7R73) of the resistor 77 is as small as possible, it is possible to secure a large operating bias voltage for the functional circuit to be connected to the current output terminal 72. By taking into account the restriction of the influence of manufacturing variations in the base/emitter voltages Vbe and the securing of the operating bias voltage of the functional circuit to be connected to the current output terminal 72, the voltage between terminals of the resistors 76 and 77 is usually set to around 0.2 V.
However, according to the conventional voltage generator using PNP transistors, as the current multiplication factor of the output circuit (a circuit consisting of the PNP transistor 58) of the error detector 55 is small (HFE=about 20 to 50), it is necessary that the output stage of the error detector 55 can bear a large inflow current. As a result, there has been a problem that the output stage of the error detector 55 becomes complex, and the cost increases. Further, according to the conventional voltage generator using NPN transistors, an NPN transistor having a relatively large base/emitter voltage Vbe flows a large output current. Therefore, there has been a problem that a maximum value of a set range of the output voltage VREG9 is lowered, and the set range of the output voltage VREG9 becomes narrow.
Further, according to the conventional current generator, the current source circuit inputs the constant voltage VREG8 (or 9) independent of temperature and a voltage power source, and the NPN transistor 73 of which base/emitter voltage Vbe has a negative temperature characteristic flows the input current Iin8. Thus, the output current I out 8 has a positive temperature characteristic. Therefore, it has not been possible to generate a constant current irrespective of temperature or power source voltage changes. It has not been possible to generate a current having a negative temperature characteristic either.
It is an object of this invention to provide a voltage generator and an output circuit for an error detector capable of reducing cost and capable of expanding a set range of an output voltage. It is another object of this invention to obtain a current generator for generating a constant current irrespective of temperature or power source voltage changes, and a current generator for generating a current having a desired negative temperature characteristic.
The voltage generator according to one aspect of this invention comprises an NPN transistor for flowing a current corresponding to a voltage output from error detecting unit; a current mirror unit having a PNP transistor, for flowing a current that is a multiple of the current that the NPN transistor flows using the PNP transistor; and a resistor for generating a feedback voltage to the error detecting unit from an output voltage generated based on a current that the current mirror unit flows.
The voltage generator according to another aspect of this invention comprises a reference voltage output unit which outputs a constant reference voltage irrespective of temperature or power source voltage changes; an error detecting unit having an output of the reference voltage output unit connected to one input; an NPN transistor having an output of the error detecting unit connected to a base; a first resistor disposed between an emitter of the NPN transistor and a low-potential side of the power source;
a first PNP transistor having a collector of the NPN transistor connected to a collector and a base, and having a high-potential side of the power source connected to an emitter; a second PNP transistor having the base of the first PNP transistor connected to a base, and having the high-potential side of the power source connected to an emitter; a second resistor disposed between a collector of the second PNP transistor and the other input of the error detecting unit; and a third resistor disposed between the other input of the error detecting unit and the low-potential side of the power source.
The voltage generator according to still another aspect of this invention comprises an NPN transistor for flowing a current corresponding to a voltage output from the error detection unit; and a current mirror unit having a PNP transistor, for flowing a current that is a multiple of the current that the NPN transistor flows using the PNP transistor.
The voltage generator according to still another aspect of this invention comprises an NPN transistor having an output of the error detection unit connected to a base; a first resistor disposed between an emitter of the NPN transistor and a low-potential side of the power source; a first PNP transistor having a collector of the NPN transistor connected to a collector and a base, and having a high-potential side of the power source connected to an emitter; and a second PNP transistor having the base of the first PNP transistor connected to a base, and having the high-potential side of the power source connected to an emitter.
The voltage generator according to still another aspect of this invention comprises a voltage generator which outputs a voltage that keeps a voltage of a feedback terminal constant irrespective of temperature or power source voltage changes; and a current source circuit having a terminal for determining an output current connected to a feedback terminal of the voltage generator, for outputting a current based on an output voltage of the voltage generator as an input.
The voltage generator according to still another aspect of this invention comprises a voltage generator which outputs a voltage that keeps a voltage of a feedback terminal constant irrespective of temperature or power source voltage changes; a first resistor having one end connected to a voltage output terminal of the voltage generator; a first NPN transistor having the other end of the first resistor connected to a collector and a base; a second resistor provided between an emitter of the first NPN transistor and a low-potential side of the power source; a second NPN transistor having a base of the first NPN transistor connected to a base; and a third resistor provided between an emitter of the second NPN transistor and the low-potential side of the power source, wherein the feedback terminal of the voltage generator is connected between the emitter of the first NPN transistor and the second resistor.
The voltage generator according to still another aspect of this invention comprises a voltage generator which outputs a voltage that keeps a voltage of a feedback terminal constant irrespective of temperature or power source voltage changes; a first resistor having one end connected to a voltage output terminal of the voltage generator; a first NPN transistor having the other end of the first resistor connected to a collector and a base; a second resistor provided between an emitter of the first NPN transistor and a low-potential side of the power source; a second NPN transistor having a base of the first NPN transistor connected to a base; and a third resistor provided between an emitter of the second NPN transistor and the low-potential side of the power source, wherein the feedback terminal of the voltage generator is connected between the emitter of the second NPN transistor and the third resistor.
The voltage generator according to still another aspect of this invention comprises a voltage generator which outputs a voltage that keeps a voltage of a feedback terminal constant irrespective of temperature or power source voltage changes; at least one diode connected in series between the voltage output terminal of the voltage generator and the feedback terminal of the voltage generator; and a current source circuit for outputting a current based on an output voltage of the voltage generator as an input.
The voltage generator according to still another aspect of this invention comprises a voltage generator which outputs a voltage that keeps a voltage of a feedback terminal constant irrespective of temperature or power source voltage changes; at least one diode connected in series between the voltage output terminal of the voltage generator and the feedback terminal of the voltage generator; a first resistor having one end connected to a voltage output terminal of the voltage generator; a first NPN transistor having the other end of the first resistor connected to a collector and a base; a second resistor provided between an emitter of the first NPN transistor and a low-potential side of the power source; a second NPN transistor having a base of the first NPN transistor connected to a base; and a third resistor provided between an emitter of the second NPN transistor and the low-potential side of the power source.
Other objects and features of this invention will become apparent from the following description with reference to the accompanying drawings.